Horizontal turbulent channel flow interacted by a single large bubble

• We focus on bubble size (1-10 mm) in events that renew turbulent shear flows.
• Influence of bubbles is represented by shear stress relative field.
• The bubbles produce two roll vortices and strong sweeping flow around them.
• High Weber number bubbles engage with two vortices to reduce friction.

Flow field modified by a single large bubble in a horizontal wall turbulent boundary layer is measured by particle tracking velocimetry. We focus on intermediate bubble size being comparable to the thickness of boundary layer to find out the events altering the original turbulent shear stress field. The results are all presented by quantities relative to single phase flow on Lagrangian grid system that moves with the bubble. The measurement results reveal bubble-produced secondary flow around itself, which involves twin roll vortices, separation on the bubble surface, and strong sweeping flow. For a small and nearly spherical bubble, the sweeping flow is provided strongly to enhance the turbulent momentum exchange while negative exchange is detected for a large flat bubble. This effective length approximately corresponds to the size of the bubble.